The oil and gas industry has for many years used hot tapping and line stop techniques in order to provide localised isolation of a “live” section of pipe.
Hot tapping involves the fitting of a branch or tee connection to a live pipeline containing fluid at pressure. The connection may be welded or mechanically secured to the pipe, a valve being subsequently fitted to the connection. A tapping or drilling tool is then connected to the valve, the tapping tool being activated to pass through the open valve and drill through the pipe wall to create the branch. The tapping tool is configured to prevent leakage of fluid from the pipe during the pipe cutting operation. On completion of the drilling process, the tapping tool may be removed and the valve closed to complete the branch connection. Thus, fluid may be selectively directed via the branch connection. Alternatively, or in addition, tools may be inserted and/or removed via the hot tap connection to perform a variety of tasks within the pipe.
Conventionally, where pipe isolation is required, a plug or line stop tool including a lip seal is inserted through the tap connection to provide uni-directional sealing isolation of the pipe inboard, or downstream, of the stopple. In order to apply a test pressure to test the integrity of the stopple seal a second opening is cut into the pipe at a location outboard, or upstream, from the first opening and a second plug or stopple put in place. A smaller third opening is drilled between the first and second openings to pressurize the isolated area between the first and second stopples, and thus pressure test the first or primary stopple seal, and also the second seal. This may only be achieved if the uni-directional lip seal arrangement of the second stopple is arranged against the prevailing pressure, that is in the opposite orientation to the first or primary seal. Thus, although two pressure-tested seals have been provided, only one, the primary seal, is effective against the isolated pressure. In addition, each intervention into the pipe requires additional planning, setup and operation time resulting in increased costs for the operator.
Applicant's BISEP double block and bleed hot tap installed isolation device, as described in GB 2,440,275, which is incorporated herein in its entirety by way of reference, provides an alternative solution. The BISEP device may be installed through a branch connection and a seal unit in the form of a spherical or globe seal module rotated to face outboard or upstream and hydraulically or otherwise activated to seal with the pipe upstream of the branch. The branch and the pipe inboard or downstream of the device are then isolated from upstream pipe pressure. The seal module carries a pair of seal elements and the module is configured such that the pressure differential acting across the module further energises the seal elements. Thus, in the event of a failure of the external seal activation, isolation is maintained. Furthermore, an annular chamber between the seal elements may be pressurised to confirm the integrity of both seal elements.
The arrangement of the seal element also permits the BISEP device to be utilised as a weld test tool, by locating the seal elements straddling a weld, and then pressurising the annulus between the seal elements.